This project is designed to provide information on the mechanisms operating within reflex systems in the spinal cord, which include alpha motoneurons as the output link, as well as on the interconnections and interactions between reflex pathways and control systems descending to the spinal cord from supraspinal centers. Particular consideration is also given to correlations between synaptic organization, intrinsic neuronal properties, and dynamic behavior of the alpha motoneurons and the motor unit type, defined by the physiological characteristics of the innervated muscle fibers.